Panthers are actually leopards (though typically not the spotted ones we usually associate with that name), so the stats there should be pretty easy. As for the dire version, Erica (DnDChick) has written a Dire Creature template that you could apply to those stats to get a Dire Panther: http://www.enworld.org/cc/converted/template/dire_creature.htm
technically I think panthers do have spots ... it's just that their coat is also black instead of yellow ... not sure if that's a real difference, but there might be a variation in the coat if you could examine closely enough ...
the MM suggests that you use leopard stats for jaguars, panthers, and mountain lions.
Actually, the leopard stats would only work for panthers, as they are infact the same animal. Jaguars are bigger and stronger than the leopard, almost as large as a lion, and would be between lions and leopards in D&D stats. Montain Lions (or pumas as they're also known) have a stockier build than leopards and are somewhat stornger, altough the two animals have roughly the same size. In D&D terms, just add two to the leopards Con and Str to get a Mountain Lion.